This invention relates to servo heads in disk file data storage systems. In particular, the present invention relates to improved passive noise cancellation in the servo heads by the use of shielding of servo heads, data heads, or both.
Disk file data storage systems contain magnetic media disks on which data is stored in concentric tracks by means of data heads which write and read magnetically encoded data. These data heads are mechanically linked to a servo head located on an electromechanical actuator. The servo head and the actuator are part of a negative feedback, closed loop servo system which is used to move the data heads (and the servo head) from one track to another for track seek operations and to hold them directly over a track for track following.
The normal output signal of the servo head is encoded radial position information, which it reads from the servo disk. However, the servo head can also pick up external electromagnetic radiation. The main source of this external electromagnetic radiation is the data head located across from the servo head. When that data head is writing data, it is also radiating noise to the servo head. The noise corrupts the normal radial position information for the servo system, thus reducing the track following precision. Consequently, the data written at that time may not be completely within the actual data track boundaries. Later, when this data is being read, the normal track following precision has returned. However, the data head is then flying within the track boundaries trying to read data which may not be written completely within the track boundaries. This increases the probability that data errors will occur during reading.
One prior art technique for canceling signals induced in the servo transducer by electromagnetic radiation emanating from the adjacent data transducer is to use a reverse wound bucking transducer. A bucking transducer can be mounted on the servo head and connected to the servo transducer in either a series-opposing or parallel-opposing configuration. The noise induced in the bucking transducer (which is generated by the adjacent data head when it is writing data) tends to cancel similar noise which is induced in the servo transducer.